The field of the invention is smoke detectors and, more particularly, smoke detectors for electrical equipment cabinets.
Commercial smoke detectors have been included in the design and installation of switch gear rooms for years. It has been assumed that the use of pendent smoke detectors provides adequate monitoring for the detection of smoke and fire in the switch gear rooms. However, such pendent mounted smoke detectors have failed to provide adequate early warning for the protection of the electrical equipment.
From experience it has been determined that the majority of smoke filled switch gear rooms are the result of electrical equipment smoldering or burning inside the switch gear. Many of the causes of insulation failure leading to such smoldering or burning have not been from short circuit problems, but rather from more subtle problems which cause excessive heating without tripping overload devices. Examples of such subtile problems include poor terminations, loose connections, misapplication of overload devices, device malfunctions, insulation breakdown of coils or control transformers, and tracking due to moisture and contamination. In addition, where there are environmental problems, such as humid locations, or where there is no provision of a controlled environment, corrosion has been a significant factor in termination problems which have led to smoldering or burning insulation.
To address such problems, maintenance programs have been established, usually consisting of surveillance and maintenance operations, including torquing of termination hardware, and infrared monitoring and photographs. All of these programs are proactive in covering an essential part of protecting the electrical equipment. Currently available reactive systems, for example, short circuit and ground fault protection, provide protection against the catastrophic failures which they are designed to protect, but do nothing to detect severe overheating caused by the factors mentioned above.
For example, a typical progression of an insulation failure is as follows. A loose connection can occur over years of service in an equipment cabinet. The loose connection can be caused by load cycling and cold flow of the conductor material in the termination, or by corrosion due to environmental conditions. In either of these cases there is not an overload condition, and thus the overload monitoring devices do not trip.
The connection point then becomes extremely hot due to the high resistance of the poor connection. With the high temperatures, the insulation of the conductors comprising the connection begins to break down and eventually will smolder or burn. This condition may escalate until there is a runaway situation in which the insulation completely fails and an arcing ground fault or phase-to-phase fault occurs. The result of such a failure is serious equipment damage as well as down time.
Conventional smoke detection systems have been particularly ineffective in detecting smoldering or burning insulation early enough to prevent such runaway failures.